Sealing agents



i atented Oct. 9,

Chester N; White, Ridley ParkfPal, assignor to sun Oil Cmpany,'Philadelphia, Pa., a corpo ration of N ew J ersey No Drawing. Application February 24', 1949, Serial No. 78,240

18 Claims; (01. 260*14) invention relates to 'a sealing-"agentfof thetype "comprising'an-aq'ueous dispersion of-a "par tially condensed thermosetting resin. More particularlyj it'relates toa--sealing agent of this type containingan' additive-material capable of rendering-that sealing agent moreuseful in the sealingot porous 'subterranean formations.

Irithe dfilling-of wells' for oil,-it is frequently advantageous to seal ofi-porous formationstraversed by the borehole. For example,*-when' formationsare encountered which are sufficientiy porous that appreciable amounts of the drilling mud pass into the formations and little or no mud l'returns-toithe surface, it is usually desirable to seal off thoseformations with a material per u to r i ef liiidss loss ordrfll- 7 ing mud is known as lost circulation and may also be due to a breakdown of formations, by the hydrostatic pressure of the mudcolum-n;

It, is also frequently advantageou'sitd'seal 'oif certain formations in order to prevent ingress of undesirable fluids, such as gasestr'water, from those formations into the well whilethe well' is being produced. Thus, water-bearing sands are often sealed off from the borehole.

Heretofore, various 'methods' have been 'employed for sealing porousformations One such methodcomprises -pumping-cement gr6ut into the Well, forcing lt into the formation, and a1- lowingit to harden. One disadvantage of this method is'that in many cases, it isimposs'ible to H controlbfiectivel'y' the extent of penetration "of cement 'into the formation'with'the result that the cement is forced in so farthat it is'difiicult to reopen the formation'by conventional meth ods, such" as fun perforation.

Another method'previously employed for'seal ingi'porous formations comprises pumping a resinefo'rming liquid into the well, forcing it into thel'formation, and allowing it'to condense and" harden at the formation temperature. With this method also,v there is the disadvantage of too deep penetration into the formation. Further-'- more, in case where very porous-formations are situated adjacent less porous-formations or where there are crevices within porous-forma tions, large amounts of resin must be forced into the more penetrable'sections of the formations before the less penetrable sections are sealed, with the result that'this method becomes'quite expensive:

A third method of the prior art comprises the use, fasi sealing'agenh'of an aqueous dispersion-iof a thermosettingresin which has bee'n partially 1. condensedzto. a particular intermediate state: i-of i condensation in which'theresin is a plastic'solid capableof being dispersed in water by stirring without the aid of an-emulsifying agent to form a suspension-which is stable for at least fivehours. In this method, when the resin has been condensedto the proper intermediate stage, the aqueous resin dispersion will, when pumped'into the welland directed against the face of the" porous-formation, forma resinplug at the face without substantial penetration of the 'resin into the body of the -formation,'even though-the pores" at th'e face are larger than-the dispersed-resinparti'cles. At the formation temperature; the resinpl-ug completes its condensationand becomes a hard-sheath impervious to drilling fluids."

Theprepara'tion" of sealing agents of the aqueous resin dispersion 'type'is disclosed and claimed by Stewart S. KurtZ et al. in the following-U. S. Patents: Reissue 23,393, July 24,

1951, reissued on application 226,064, filed-May 12, 1951, the original patent being No. 2,457,160 issued December 28, 1948, from application-Serial No.'609,927, filed August 9,1945; 2,562,866, issued July 31, 1951, from application serial No. 54,586, filed October 14, 1948; 2,562,867, issued July 31, 1951, from application Serial-No. 54,587, filed October 14, 1948; 2,559,162, issued July 3, 1951, fr'omlapplication Serial No. 54,588, filed October 14, 1948.

The following are'given as examplesof materials which may be reacted under condensation conditions to give 'thermosetting'resins having the properties described above: phenol or cresylic acid and 1-4 parts of formalin or furfural, one part of melamine "and /6-29 parts of formalin, one part of melamineand 1-8 parts of'iurfura-l,- one part of "urea and 1 -2 parts of formaline, onepart ofurea and 1-6 parts of furfu'ral, one part of thio urea and A3-5 parts of formalin, and one part ofthiourea and /2-6 parts of furfural. v I K p g V p I I have discovered that theaddition wan-aqua ous resin dispersion sealingag entof a Water soluble or water-dispersible polysaccharide having a molecular weight greater than about 5000 is especially'efictive to decrease theamount of water which will pass from the sealing: agent through a "given porous bed when: thesealir'lg agent is "applied'thereto at a givenpressure, thus reducing the 'amount of these'aling'fagent re-" quired to seal off the bed: Also," formations of greater'porosity may be sealed off by a -given sealing agent of the'aqueous resindispe'rsiontype 1 if such a polysacc'haride is incorporatedihere withz The term polysaccharide, where usedin one part ofthis specification, refers to a carbohydrate containing a plurality of molecules of simple sugars. High molecular weight polysaccharides which are suitable for use in the invention include those which contain a substantial number of neutralized carboxylate groups per molecule, and those which contain no substantial number of carboxylate groups. The latter polysaccharides include such materials as agar-agar, starch, and cellulose. The former include the sodium salt of carboxy methyl cellulose, and natural gums, which contain metal salts of uronic acids.

Water-soluble or water-dispersible natural gums, as contemplated in the invention, include those excretions from plants which either swell in water or form colloidal solutions therewith, which are viscous and glutinous when moist, and which contain complex organic acids which hydrolyze to simpler acids and certain sugars. Among the natural gums which are useful in the invention, certain ones are preferred in that the aqueous resin dispersions containing them form plugs which will set to a hard strong sheath when cured at 100 F. for 48 hours under 500 pounds per square inch differential pressure. These preferred gums include gum arabic, manila gum, and tragacanth gum. Other gums such as gamboge, ghatti gum, and karaya gum, improve the plugging properties of an aqueous resin dispersion and are therefore useful in the invention, but they are not preferred because the resulting sealing agents form resin plugs which do not form hard strong sheaths when cured under these conditions. although a hard sheath is desirable in some cases, a plug having less mechanical strength is useful in some applications of the invention.

It is to be noted that the natural resins, a group of high molecular weight materials of a non-polysaccharide nature, such as camphor, catechu, copal, dammar, elemi, guaiacum, mastic, sandarac, and shellac, are not suitable for use It is to be noted that,

in the invention, in that they give relatively lit-p tle, if any, reductions in filtrate volume when used as additive materials for aqueous synthetic resin dispersion sealing agents.

The sealing properties of an aqueous resin dispersion, with which has been incorporated a high molecular weight polysaccharide, according to the invention, improve with increasing concentration of polysaccharide in the sealing agent. Generally speaking, the rate of improvement in sealing properties decreases with increase in polysaccharide concentration; and is such that no material benefit attends the use of more than 20% by weight of the additive, although other concentrations naturally are not excluded from the scope of the invention. In most instances, a practicably useful concentration will be found in the range from about A.; to about 10% by weight.

The following examples are presented as illustrative of the invention:

Example I Aqueous dispersions of partially condensed phenol-formaldehyde resins were prepared according to the procedure described in U. S. Patent No. 2,457,160. In the preparation of the resin, the ratio of phenol to formalin was 1 to 3. The reaction was carried out in the pres ence of caustic soda at a temperature of 95 C.-100 0., and was interrupted by separation and sudden cooling of the resin phase after 200 minutes reaction time. The synthetic, resin product was dispersed in water by mechanical agitation without the use of an emulsifying agent.

To dispersions thus prepared were added various polysaccharides in 3% concentration. The dispersions were mixed under mechanical agitation to give the sealing agents listed in the table below.

The sealing properties of each sealing agent were determined for a sand bed composed of 2040 mesh particles. The bed was about two inches in depth and 0.6 square inch in crosssectional area.

In each run, the sealing agent to be tested was introduced into the space above the filter bed in the vessel containing the latter. A differential pressure of about 730 millimeters of mercury was applied across the filter bed for a period of 30 minutes. Unfiltered sealing agent was present above the bed during the entire 30 minutes. The amount of liquid passing through the bed in 30 minutes was collected and its volume measured, as recorded in the table below.

Subsequently, the resin plug in the upper part of the sand bed was cured at F. for 48 hours under 500 pounds per square inch differential pressure, in order to determine the nature of the ultimate filter cake. The quality of the filter cake obtained in each case is recorded in the The high molecular weight polysaccharide additives gave reductions in filtrate volume in the range 79-100%.

Certain of the sealing'agents require higher temperatures for curing and therefore showed imperfect or no curing under the conditions of this example.

Of the polysaccharide materials; sodium carboxy methyl cellulose and several gums effected a seal immediately and allowed no appreciable filtrate at 30 millimeters pressure. Of these gums, however, only-tragacanth gave a sealing agent capable of forming a hard strong sheath on curing under the conditions of this example.

By way of comparison, yellow dextrine (a polysaccharide having a molecular weight less than 5000) gave very little reduction in filtrate volume.

gave an 87% reduction.

Example II Aqueous dispersions of partially condensed phenol-formaldehyde resins were prepared as in Example I. To each was added gum arabicin varying concentrations. The sealin properties of each sealing agent thus prepared were deter? mined for a 20-40 mesh bed as in Example I;

Thin boiling starch (a polysaccharide having a molecular weight greaterthan 5000) The amounts ofliquid .passingthrough the bed in each run are listed in thetable belowz.

' I Volume of Fil- Concentration Hate Through, of Gum Arabic, 20410 Mesh Bed inPerOent 1n Mlllillters It may be seen from the above table that the ability of the sealing agent to seal oil a 20-40 mesh bed increases with increasing concentra-. tions of the additive. The rate of increase in sealing ability, however, decreases with increasing additive concentrations.

Example III thiourea-aldehyde;resin, partiallyr 20311519 8139? 9. the intermediate plastic solid: stage at whichthe resin is dispersiblein, water by stirring without the aid of an emulsifying agent to form a noncolloidal suspension, said. aqueous suspension beingcharacterized by its ability, when forced into a bed of 10 mesh sand, to form a resin plug at the face of the bed, which, upon application of heat, will condense to a hard layer impervious to drilling fluid.

2. Sealing agent according to claim 1 wherein the polysaccharide is a natural gum.

3. Sealing agent according to claim 1 wherein the polysaccharide is tragacanth gum.

4. Sealing agent according to claim 1 wherein the polysaccharide is gum arabic.

5. Sealing agent according to claim 1 wherein the polysaccharide is a sodium salt of carboxy methyl cellulose.

6. Sealing agent according to claim 1 wherein the polysaccharide is agar-agar.

'7. Sealing agent according to claim 1 wherein the polysaccharide is starch.

8. Sealing agent according to claim 1 wherein the polysaccharide comprises less than about of the sealing agent.

9. Sealing agent according to claim 1 wherein the polysaccharide comprises about A; to about Volume of Filtrate in Milliliters Additive, 3% Concen- 16-20 10-16 .6-10 4-6 M Inch, egg was Mesh Mesh Mesh Mesh 4 Mesh Inch Inch N o additive. 757 720 l, 600 4, 400 Agar-agar. 8 20 26 20 4, 400 Gum arabic 82 135 122 160 145 Manila gum- 255 274 281 265 Tragacanth 0 5 16 38 175 Ghatti gum 0 18 15 l, 600 4, 400 Karaya 0 0 4, 400 Thin-boiling starch 66 125, l. 600 Sodium carboxy methyl cellulose 7 190 Gamboge 15 The above table demonstrates the fact that, in general, the ability of a sealing agent to seal ofi a sand bed decreases as the size of the bed particles increases. With certain types of polysaccharides as additives in 3% concentration, there are critical porosities; that is, with sand beds of porosity greater than a certain value, the amount of filtrate obtained suddenly increases to an amount approximately the same as that obtained without an additive in the sealing agent. Within the ranges of bed porosities tested, that is true of agar-agar, ghatti gum, karaya, and thin-boiling starch.

In some cases, in the preceding examples, where the filtrate volumes were relatively large, the values given in the table were estimated by measuring filtrate volumes for a period less than thirty minutes and multiplying that volume by the ratio of thirty to the lesser period.

In some cases, where filtrate volumes obtained with sealing agents containing additives were very large, the values given were estimated from filerate volumes obtained with the resin dispersion alone.

I claim:

1. A sealing agent comprising in stable admixture a minor proportion of a polysaccharide having amolecular weight greater than about 5000 and a major proportion of a non-colloidal aqueous suspension of dispersed condensation-type thermosetting resin selected from the group consisting of phenol-aldehyde, cresylic acid-aldehyde, melamine-aldehyde, urea-aldehyde, and 76 10% of the sealing agent.

10. A sealing agent comprising in stable admixture a minor proportion of a polysaccharide having a molecular weight greater than about 5000 and a major proportion of a non-colloidal aqueous suspension of dispersed phenol-formaldehyde resin partially condensed to the intermediate plastic solid stage at which the resin is dispersible in water by stirring without the aid of an emulsifying agent to form a non-colloidal suspension, said aqueous suspension being characterized by its ability, when forced into a bed of 10 mesh sand, to form a resin plug at the face of the bed, which, upon application of heat, will condense to a hard layer impervious to drilling fluid.

11. Sealing agent according to claim 10 wherein the polysaccharide is a natural gum.

12. Sealing agent according to claim 10 wherein the polysaccharide is tragacanth gum.

13. Sealing agent according to claim 10 wherein the polysaccharide is gum arabic.

14. Sealing agent according to claim 10 wherein the polysaccharide is a sodium salt of carboxy methyl cellulose.

15. Sealing agent according to claim 10 wherein the polysaccharide is agar-agar.

16. Sealing agent according to claim 10 wherein the polysaccharide is starch.

17. Sealing agent according to claim 10 wherein the polysaccharide comprises less than about 20% of the sealing agent.

18. Sealing agent according to claim 10 where- REFERENCES CITED The following references are of record in the file of this patent:

Number 8 UNITED STATES PATENTS Name Date Dent Jan. 26, 1937 Alexander June 10, 1941 Menger June 10, 1941 Lerch May 16, 1944 Bass Feb. 2 7, 1945 Kurtz, Dec. 28, 1948 

1. A SEALING AGENT COMPRISING IN STABLE ADMIXTURE A MINOR PROPORTION OF A POLYSACCHARIDE HAVING A MOLECULAR WEIGHT GREATER THAN ABOUT 5000 AND A MAJOR PROPORTION OF A NON-COLLOIDAL AQUEOUS SUSPENSION OF DISPERSED CONDENSATION-TYPE THERMOSETTING RESIN SELECTED FROM THE GROUP CONSISTING OF PHENOL-ALDEHYDE, CRESYLIC ACID-ALDEHYDE, MELAMINE-ALDEHYDE, UREA-ALDEHYDE, AND THIOUREA-ALDEHYDE RESIN, PARTIALLY CONDENSED TO THE INTERMEDIATE PLASTIC SOLID STAGE AT WHICH THE RESIN IS DISPERSIBLE IN WATER BY STIRRING WITHOUT THE AID OF AN EMULSIFYING AGENT FO FORM A NONCOLLOIDAL SUSPENSION, SAID AQUEOUS SUSPENSION BEING CHARACTERIZED BY ITS ABILITY, WHEN FORCED INTO A BED OF 100 MESH SAND, TO FORM A RESIN PLUG AT THE FACE OF THE BED, WHICH, UPON APPLICATION OF HEAT, WILL CONDENSE TO A HARD LAYER IMPERVIOUS TO DRILLING FLUID. 